Automotive ignition contact point



Feb. 15, 1954 w HARTMAN, JR 2,669,633

AUTOMOTIVE IGNITION CONTACT POINT Filed Aug. 22, 1952 r" Fi Y F8 9- 5 (B .2 Z 51111111153011!!! l (B I V 6) Ft r. 4 2

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HTTOF/VE) Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE AUTOMOTIVE IGNITION CONTACT POINT Application August 22, 1952, Serial No. 305,720

4 Claims.

This invention relates to improvements in ignition contact points for automotive ignition systems. In the contact points now in use, specifically shown in Patent #2,072,112 to King, dated March 2, 1937. a hollow contact 20 engages a solid contact 2'5. The metal vaporized by arcing between the contacts migrates predominantly from the positive to the negative contact in the above instance, or from the solid to the ventilated disc. It is the current practice to out thin (0.035") discs from swaged sintered tungsten rod stock, which by virtue of the manner in which it is made, has the grain structure oriented perpendicular to the contact face. Half of these discs are used for the solid or negative contacts after surface finishing, but those which are to become ventilated contacts must be perforated individually in an extra operation. This second process is very costly because the discs must be handled by hand or by a very complex automatic device. In either case, the scrap rate and the resulting cost of manufacture is too high. This has resulted in limiting the application of the King invention.

I have discovered a method by which ventilated contacts made from punchings out of thin strip tungsten may be used without sacrificing any of the advantages of contacts made from out rod. These contacts can be made much more economically because strip stock can be handled in automatic punch presses of standard construction and the second handling of the solid disc necessary to make the vent hole is eliminated. Although the resistance to transfer of punched strip tungsten contacts is less than that of cut rod contacts due to the grain in the former being oriented parallel to the contact face, I have found that by mounting the punched contact so that it is of negative polarity in operation, the transfer action tends to coat it with a layer of metal from the mating contact and thus, it is not exposed to erosion. The useful life of this assembly is, therefore, essentially equal to the more costly construction in which both the solid and ventilated contacts are made from out rod stock.

Another change from the King disclosure was to increase the area of the opening about ten or eleven times. King teaches (page 3, line 35 of column 2) that:

The diameter of this vent is shown exaggerated in the drawing for clearness, but it should actually be about .040 to .050" in diameter, according to the results of tests already made.

Measuring the disclosure, King shows an area of the opening of 3 of total area of the contact. teaching is around 2%. I have found an area of the opening should he 20%plus or minus 5%that is, an area substantially 900% greater.

Figure 1 illustrates the direction of the grain when the material is rolled into sheets .035" thick and the method of stamping the hollow contacts.

Figure 2 shows the direction of the grain in the rods 0.200" in diameter.

Figure 3 shows a cross-sectional elevation of a pair of contacts in which the hollow contact is stationary.

Figure 4. shows a cross-sectional elevation on plane 4-4 of Figure 3 of the movable positive contact.

Figure 5 shows a cross-sectional elevation of a pair of contacts in which the solid positive contacts are stationary.

Figure 6 is a cross-sectional elevation through plane 6--6 of Figure 5.

Figure 7 illustrates the transfer of metal from the solid cut rod contact to the hollow contact.

In the figures:

A is the rolled sheet .035" thick with the grain running parallel with the face of the sheet. B is an annular stamping 0.200" in diameter. C is the central portion.

In Figure 2, D is a swaged rod 0.200" in diameter with the grain running parallel with the axis of the rod. The broken lines indicate that it is cut with a cutting wheel 0.035" approx. lengths. E is the stationary support for B.

In Figure 3, F is the oscillating arm of the ignition system. It carries the solid contact point D, which is positive.

Figure 4 shows a cross-section on a plane at right angles to the plane of Figure 3. The arm F is brazed to a solid contact point D which has the grain running at right angles to the contact face.

Figure 5 is an alternative construction in which the solid contact is stationary and the hollow contact is mounted on a movable arm.

However, this is exaggerated so the King Figure 6 shows a channel sectioned arm G supporting the hollow negative contact B.

Figure 7 shows the transfer of the better metal on the solid positive contact to the relatively inferior metal of the annular contact point B mounted on the bracket E. The following dimensions have been found satisfactory:

B equals 0.200".

equals 0.090".

D equals 0.200". Thickness of B and D equals 0.035". The area of C equals .00633 sq. inch. The area of B equals .03142 sq. inch. Ratio of C B equu. 1s.20 ;(g%f" Kin izlshows Cbquals 0.001135 sqr' nch.

w en B equals'0.03142 sq. inch". Ratio of C B equals 3.6%.

King teaches C" equals .000615 sq. inch when B equals .03142 sq. inch Ratio of C" B equals less than 2% The results flowing from this increase in areahavebeen a factor in converting failure into success.

What I claim is:

1. In a high tension ignition system for internal combustion engines including a circuit breaker having a fixed contact support anda movable contact support, the improvement.comprising; a pair of sintered metal contacts carried by said contact supports, said contacts com? prising a first. disc shaped contacthaving asub-v stantially planar contact surface and a central aperture therethrough, thegrain of thesintered approximately.

metalinsaid firstcontact. being-parallel .to. its,

contact surface, and a second solid disc shaped contacthaving a substantially planar contact surface for. contact with the contact surface of said first contact, the grain of the sintered metal in said second contact being perpendicular to its contact surface.

2. In a high tension ignition system for internal, combustion engines including a circuit;

breaker having a fixed contact support and a movable contact support, the improvement comprising; a pair of sintered metal contactscarried by said contact supports, saidcontacts comprising a first disc shaped contact having a substantially planar contact surface and a central aperture-therethrough,.the areaof said aperture in the plane of, the contact surface being from substantially to 25 percent of the total area of the contactsurface, the grain of. the sintered metal .insaid first contact being parallel to its contact surface, and a second solid diskshaped contacthavinga substantially, planar. contact surface for contact with the contact surface of said first contact, the grain of the sintered metal in said second contact being perpendicular to its contact surface.

3. In an ignition system for internal combustion engines including a circuit breaker having a fixed contact support and a movable contact support, the improvement comprising; a pair of sintered metal contacts carried by said contact supports, said contacts comprising a first disc shaped contact having a substantially planar contact surfacerandea central. aperture therethrough, the area of said aperture in the. plane of the contact surface being substantially 20 per- -cent of the total area of the contact surface, the

grain of the sintered metal in said first contact being parallel toits contact surface, and a second-soliddisk shaped contact having a substantially .planar contact surface for contact with the contact. surfaceof said first contact, the grain of the sintered metal in said second contact' being'perpendicular to its contact surface.

4. In, an'ignition system for internal combustion engines including a circuit breaker having a fixed contact support and a movable contact support, the improvement, comprising; a pair of sintered metal contacts carried by said contact supports, saiducontacts.comprising a first disk shaped. contact having a substantially planar contact surface and a centralaperture therethrough, the area of said aperture in the plane of the contact surface being from substantially 15 to 25 percent of the total area of the contact surface, the grain of the sintered metal in said firstcontact being parallel to its contact surface, anda second soliddisk shaped contact. having a substantially planar. contact surface for contact with the contact surface of said first contact, the grain. of the sintered metal in said second contact being perpendicular to its contact surface.

FRANK W.'HAR'IMAN, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,072,112 King Mar. 2, 1937 2,486,341 Strumbock Oct. 25, 1949 

